1. Field of the Invention
The present invention relates to devices for treating femoral fractures.
2. Description of the Prior Art
There are a variety of devices used to treat femoral fractures. Fractures of the neck or head, as well as intertrochanteric fractures of the femur have been successfully treated with a variety of compression hip screw assemblies which include generally a compression plate having a barrel member, a lag screw and a compressing screw. The compression plate is secured to the exterior of the femur and the barrel member is inserted into a predrilled hole in the direction of the femoral head. The lag screw which has a threaded end and a smooth portion is inserted through the barrel member so that it extends across the break and into the femoral head. The compressing screw connects the lag screw to the plate. By adjusting the tension of the compressing screw the compression (reduction) of the fracture can be adjusted. The smooth portion of the lag screw must be free to slide through the barrel member to permit the adjustment of the compression screw. Because the barrel member is long in comparison to its diameter, the force required to slide and, therefore, maintain reduction of the fracture is minimal. However, compression hip screw assemblies require a long incision in the tissue around the fracture and the compression plate, positioned on the outside of the bone, is displaced from the application of force thereby creating a long moment arm and subjecting the implant to very high tensile forces.
Compression hip screw assemblies are shown by the following patents: Fixel, U.S. Pat. No. 4,432,358; Calender, Jr., U.S. Pat. No. 3,374,786; Pugh et al., U.S. Pat. No. 2,702,543; Griggs, U.S. Pat. No. 4,530,355; Blosser, U.S. Pat. No. 3,094,120; and Wagner, U.S. Pat. No. 3,842,825. The Blosser and Wagner patents illustrate the use of multiple screws to prevent rotation of the lag screw relative to the compression plate and barrel member. A surgical bone pin which functions like a lag screw and compressing screw but which does not include a compression plate is shown by Cochran et al., U.S. Pat. No. 3,103,926.
Subtrochanteric and femoral shaft fractures have been treated with the help of intramedullary rods which are inserted into the intramedullary canal of the femur to immobilize the femoral parts involved in fractures. A single angled cross-nail or locking screw is inserted through the femur and the proximal end of the intramedullary rod. In some varieties, one or two screws may also be inserted through the femoral shaft and through the distal end of the intramedullary rod. The standard intramedullary rods have been successfully employed in treating fractures in lower portions of the femoral shaft.
The Grosse-Kempf nail manufactured by Howmedica Company of Rutherford, New Jersey is believed to be one of the earliest intramedullary nailing devices introduced into the United States. The Grosse-Kempf nail includes a threaded hole in the intramedullary rod for receiving the interlocking screw. The fully threaded screw cannot slide through the threaded hole to permit the type of compression found in the compression hip screw assemblies discussed above. Furthermore, the axis of the threaded hole coincides with a line between the greater to lesser trochanter and not in the direction of the femoral neck.
Zickel, U.S. Pat. No. 3,433,220, which issued on Mar. 18, 1969, discloses an intramedullary rod and cross-nail assembly which is useful in treating fractures occurring in the upper one-third or subtrochanteric portion of the femur. The Zickel nail is a solid intramedullary nail having a single proximal tri-flange cross-nail which is inserted in the direction of the femoral head.
The rigid tri-flange cross-nail is not suitable for use in treating femoral neck fractures because the cross-nail must be locked into position by a set screw to prevent backing out. Adequate compression cannot be achieved. As stated above, the sliding compression screw has been found to be most effective in treating femoral neck fractures.
A femoral fracture device which includes an intramedullary rod and a screw inserted through the proximal portion of the rod in the direction of the femoral head which is designed to permit sliding compression of selected fractures is described in Brumfield, U.S. Pat. No. 4,827,917. The device of the Brumfield patent combines the superior mechanical and biological attributes of intramedullary fixation with the proven benefits of the sliding compression screw.
An object of the present invention is to improve upon the benefits achieved by the Brumfield patent by more closely providing the slidability and consequent reduction of the fracture heretofore available only with conventional compression hip screw assemblies.